Wireless power transfer is expected to become increasingly popular, for instance for wireless battery charging of mobile devices such as, for instance, mobile terminals, tablet computers, laptop computers, cameras, audio players, rechargeable toothbrushes, wireless headsets, as well as various other consumer products and appliances.
The Wireless Power Consortium has developed a wireless power transfer standard known as Qi. Other known wireless power transfer approaches include Alliance for Wireless Power, and Power Matters Alliance.
The wireless power transfer standard known as Qi by the Wireless Power Consortium will be referred to, without limitation, throughout this document as the presently preferred wireless power transfer manner applicable to the present invention. However, the invention may generally be applied also to other wireless power transfer standards or approaches, including but not limited to the ones mentioned above.
Operation of devices that comply with Qi relies on magnetic induction between planar coils. Two kinds of devices are involved, namely devices that provide wireless power (referred to as base stations), and devices that consume wireless power (referred to as mobile devices). Power transfer takes place from a base station to a mobile device. For this purpose, a base station contains a subsystem (a power transmitter) that comprises a primary coil, whereas a mobile device contains a subsystem (a power receiver) that comprises a secondary coil. In operation, the primary coil and the secondary coil will constitute the two halves of a coreless resonant transformer.
Typically, a base station has a flat surface, on top of which a user can place one or more mobile devices so as to enjoy wireless battery charging or operational power supply for the mobile device(s) placed on the base station.
During operation, heat will be generated by magnetic induction in the secondary coil of the power receiver, i.e. in the mobile device. Moreover, the power transmitter in the base station will generate heat that will be conveyed from the base station to the mobile device. If the thermal exposure for the mobile device becomes excessive, several undesired effects may arise. For instance, vital components may be damaged in the mobile device, such as for instance a lithium ion battery or electronic circuitry in a smartphone. At severe overheating, objects in the vicinity of the mobile device may be damaged and even cause a fire or toxic smoke hazard. Furthermore, the duration of the charging period may be prolonged, since protective circuitry in the mobile device may intervene to reduce or even suspend the charging power until the temperature has been reduced again. Also, the intended user will become generally suspicious and assume a somewhat negative position with respect to the mobile device (or the base station) if the mobile device is too hot when picked up from the surface of the base station.
There is therefore a need among different interest groups to test, measure, evaluate, emulate or otherwise assess the thermal exposure of a mobile device when being subjected to wireless power transfer from a wireless power transmitter. Such interest groups may for instance involve any of the following: developers, manufacturers or suppliers of mobile devices; developers, manufacturers or suppliers of wireless power transmitter devices; test or compliance entities in the field of wireless power transfer; and test or compliance entities in the field of consumer product safety.